I am performing some CV on organic electrochromic material with three -electrode scheme. ITO with spincoated polyviologen as an working electrode, Ag/AgCl wire in a 3.5 M KCl (aqu) solution as a reference electrode and Pt wire as an counter-electrode. Electrolyte: 0.1 M aqu KCl.
Run the CV with bare ITO as working and check where are the limits (you'll see the proton reduction somewhere at negative potentials and water oxidation at quite positive ones). Then repeat with the spincoated and you will see the signals from the viologen usually around -600 and -900 mV.
In general the oxygen evolution reaction in the anodic direction, and the hydrogen evolution in cathodic ... in between you should find your reactions ...
Water decompose into O2 at -1.23 V, but this is only possible at standard condition. Your working electrode is different and you are also not using any buffer. In that case you just run the supporting electrolyte solution and find the potential window as Edward suggested.
Thank you! But what should I use in this supproting electrolyte CV as an working electrode? Bare ITO? Or may be simply Pt wire? Because I've read that ITO also interact with water (and water electrolytes) under negative potentials.
Run the CV with bare ITO as working and check where are the limits (you'll see the proton reduction somewhere at negative potentials and water oxidation at quite positive ones). Then repeat with the spincoated and you will see the signals from the viologen usually around -600 and -900 mV.
you can chec the potential limit with the ITO electrode you will see the anodic current corresponding to the oxygen evolution with the same maner you will see the cathodic current for hydrogene evolution at the cathodic side . then you can identify the potential range of your work.
The window will depend to some degree on the working electrode, consider for a moment a mercury electrode for this electrode you can go to a far more reducing potential in water as the exchange current density for proton reduction is much smaller than it is on Pt.
You are right Mark. Proton reduction and oxygen evolution depends on the substrate nature, as long on the electrolyte pH. Mikhail should stablish pH condition and then run CV with both electrodes for the electroactivity window limits.
As far as I know ITO is not the best choise for cathodes in water. In our experiments at certain cathodic potential (don't remember the value) it becomes dark and losees transparency
Normally your aqueous electrolyte will start decomposing at just between 1.1-1.3V. So the best way to start, is to run a CV anywhere between 0.0 to 0.5V and increase your potential window by 0.1V to the anodic side until just before the oxygen evolution begins, and do the same to the cathodic side until hydrogen evolution start taking place. Then you can use any potential window in between for your experiments (before oxygen and hydrogen evolution).
Whenever, we study electrochemical behaviour of any CP in aq. electrolyte, we look for the redox behaviour of the polymer and potential window of the electrolyte. We have to be careful about the O2 and H2 evolution at respective anode and cathode. Generally in anodic side, we should not exceed the limit to +1.2 V vs Ag/Ag+. The negative limit should be restricted to -0.2 to -0.3 V.
Dear brother, The limits are dependent on electrochemical stability of the solvent, water splits above 3V, so its limits are -2.5 to 3V. if you want to scan above 3V, you will have to change the solvent.
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